Helical Focuser Adapter for Compact Guidescope

thingiverse

A readily available, affordable 190mm f/3.8 guidescope often lacks any mechanism for focusing except by screwing in and out the objective lens or sliding the guide camera into the 1.25" eyepiece opening. I was unable to focus without a bothersome 5mm extension and even then it was somewhat unreliable at best. A premium version of this guidescope is available but so too are aftermarket helical focusers designed specifically for guidescopes. The two do not interface seamlessly without some special adapter that nobody appears to sell. The ID of the guidescope tube features a very inconvenient 50.5 - 51mm x0.75mm thread and the focuser will only screw into a M36x1mm thread. I discovered a precise offset allowing full focus range of approximately 15ft to infinity (and beyond). The adapter flange is slotted to facilitate installation or removal. After at least six revisions, it fits and functions well.